Such bags conventionally are of rectangular configuration formed from an elongate plastic sheet or film folded upon itself to form two panels and sealed together along their opposite side edges with an opening defined by the free edges of the panels. The opening is adapted to be repeatedly opened and closed by closure/sealing means formed from a rib extending across one of the panels below the opening of the bag and inter-engaging in a groove formed between, and therefore defined by, two ribs extending across the other panel and also below the opening of the bag. Two parallel extending ribs on either sides of the rib which engages within the groove serve to capture the ribs within the defined groove.
The ribs and grooves are shaped and dimensioned so that the rib fits tightly within its associated groove and the ribs defining the associated groove deform to allow the rib to enter and to be captured within its associated groove. The bag is opened by gripping the free edges of the panel at the opening of the bag and pulling the panels apart with the rib disengaging from its associated groove thereby allowing access to the interior of the bag to receive or retrieve contents. To close or reseal the opening to the bag one end of the rib is pressed by thumb and finger pressure into the adjacent end of the associated groove with the thumb or finger under pressure being subsequently drawn along the length of the rib and groove arrangement to progressively introduce the rib into its associated groove to be tightly received therein and whereby to seal the opening of the bag.
The opening of the bag can be repeatedly opened and closed as required, with the closure process being analogous to that accomplished by a zipper and thus the term “zipper” is sometimes used to describe such reclosable bags.
With known reclosable or “zipper” bags, the portions of the two panels adjacent there free edges, and above the rib/groove closure means, have a plurality of parallel shallow ribs formed across the opening, usually on the inside of the panels, to allow secure finger gripping when those portions of the panels are gripped to pull the panels apart and disengage the closure means when opening the bag.
Reclosable bags, which are extruded through a die head have an area of weakness below the closure, that is, the bags are flimsy due to the thickness of the plastic sheet or film used to form the bag, and the plastic panels split or break below and/or above the closure if it is too tight and/or the user applies and/or maintains undue force when opening the bag, that is, the user is aggressive. But on the other hand for security, water tightness, and air tightness, a tight closure is required. In addition, the flimsy nature of the extruded closures makes them harder to engage and seal when closing. The filmsy nature of the material also makes it harder to control closure quality during production.
One solution to this problem has been to form the panels adjacent to closure from a plastic laminate with a profiled closure which provides added strength to resist splitting or breaking of the panels in the area of the closure, whilst the additional rigidity provided by the laminate makes it easier to engage the closure and seal the opening of the bag.
However, with reclosable bags having laminated plastic for the panels adjacent to closure means, the manufacturing costs are higher than for extruded closure bags because of the more sophisticated manufacturing equipment required, as well as the additional material costs, all adding to the cost of the bag to the consumer as compared with a bag having a simple extruded closure. There are also a limited number of suppliers of profiles to be used with a laminated construction, due to the very expensive set up costs for the production of profiles which are essential for a laminated construction.
It is therefore an object of one preferred embodiment of the present invention to provide a reclosable plastic bag having a closure formed by the simpler extrusion process and therefore without the additional cost factors associated with the laminated plastic alternative, but which also minimises, or eliminates, the problems with bags with conventional extruded closures.